The present invention relates generally to a magnetic recording and reproducing device and more particularly, to the construction of a bearing which supports, by a hydraulic bearing a high precision rotation transmission device such as a cylinder in a video tape recorder (VTR).
The rotary head assembly of VTR must maintain the relative velocity and position between a head and a tape with higher degrees of accuracy and must reproduce them with a higher degree of fidelity. However, in order to satisfy the demand for recording with a higher degree of density so as to increase the recording and reproducing time interval, the prior art rotary head assembly of the type which uses the rolling contact bearings has been found unsatisfactory. Therefore, in order to attain the accurate rotation, there have been proposed various types of rotary head assemblies using the hydraulic bearings. In case of the commercial VTR, however, there arises a difficult problem how to seal a predetermined quantity of lubricating oil with a low viscosity in a cylinder without leakage. Furthermore, in order to carry out the required performance, the rotary head assembly with the hydraulic bearings becomes very complex in construction. The commercial VTR sets must be mass produced with low costs. Otherwise, they have no commercial value at all. In order to solve the above and other problems, there have been devised and demonstrated various rotary head assemblies with the hydraulic bearings. For instance, a copending U.S. Patent application Ser. No. 4,564 now U.S. Pat. No. 4,251,840, '79 discloses a rotary head assembly with hydraulic bearings. The upper and lower cylinders of the VTR rotary head assembly along which travels the tape in contact therewith are made of aluminum with is non-magnetic and highly resistive to corrosion and has a lower coefficient of thermal expansion. The shaft is made of steel with a higher modulus of longitudinal elasticity so that the rigidity of the rotating member can be attained. The upper and lower cylinders and the shaft are different in coefficient of thermal expansion so that even when the relative position between the tape and the head is correctly determined at room temperature, it varies with temperature variation. Since there has been a strong tendency toward the decrease in track width on the tape so that a high density recording can be attained, the tracking error between the head and the tape must be minimized as much as possible.